2,209 research outputs found
Inference of dynamic systems from noisy and sparse data via manifold-constrained Gaussian processes
Parameter estimation for nonlinear dynamic system models, represented by
ordinary differential equations (ODEs), using noisy and sparse data is a vital
task in many fields. We propose a fast and accurate method, MAGI
(MAnifold-constrained Gaussian process Inference), for this task. MAGI uses a
Gaussian process model over time-series data, explicitly conditioned on the
manifold constraint that derivatives of the Gaussian process must satisfy the
ODE system. By doing so, we completely bypass the need for numerical
integration and achieve substantial savings in computational time. MAGI is also
suitable for inference with unobserved system components, which often occur in
real experiments. MAGI is distinct from existing approaches as we provide a
principled statistical construction under a Bayesian framework, which
incorporates the ODE system through the manifold constraint. We demonstrate the
accuracy and speed of MAGI using realistic examples based on physical
experiments
Mutual-Chern-Simons effective theory of doped antiferromagnets
A mutual-Chern-Simons Lagrangian is derived as a minimal field theory
description of the phase-string model for doped antiferromagnets. Such an
effective Lagrangian is shown to retain the full symmetries of parity,
time-reversal, and global SU(2) spin rotation, in contrast to conventional
Chern-Simons theories where first two symmetries are usually broken. Two
ordered phases, i.e., antiferromagnetic and superconducting states, are found
at low temperatures as characterized by dual Meissner effects and dual flux
quantization conditions due to the mutual-Chern-Simons gauge structure. A dual
confinement in charge/spin degrees of freedom occurs such that no true
spin-charge separation is present in these ordered phases, but the spin-charge
separation/deconfinement serves as a driving force in the unconventional phase
transitions of these ordered states to disordered states.Comment: 16 pages, 2 figures; published versio
Microstructural characterization of AISI 431 martensitic stainless steel laser-deposited coatings
High cooling rates during laser cladding of stainless steels may alter the microstructure and phase constitution of the claddings and consequently change their functional properties. In this research, solidification structures and solid state phase transformation products in single and multi layer AISI 431 martensitic stainless steel coatings deposited by laser cladding at different processing speeds are investigated by optical microscopy, Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), orientation imaging microscopy (OIM), ternary phase diagram, Schaeffler and TTT diagrams. The results of this study show how partitionless solidification and higher solidification rates alter the microstructure and phase constitution of martensitic stainless steel laser deposited coatings. In addition, it is shown that while different cladding speeds have no effect on austenite–martensite orientation relationship in the coatings, increasing the cladding speed has resulted in a reduction of hardness in deposited coatings which is in contrast to the common idea about obtaining higher hardness values at higher cladding speeds.
Superconducting ground state of a doped Mott insulator
A d-wave superconducting ground state for a doped Mott insulator is obtained.
It is distinguished from a Gutzwiller-projected BCS superconductor by an
explicit separation of Cooper pairing and resonating valence bond (RVB)
pairing. Such a state satisfies the precise sign structure of the t-J model,
just like that a BCS state satisfies the Fermi-Dirac statistics. This new class
of wavefunctions can be intrinsically characterized and effectively manipulated
by electron fractionalization with neutral spinons and backflow spinons forming
a two-component RVB structure. While the former spinon is bosonic, originated
from the superexchange correlation, the latter spinon is found to be fermionic,
accompanying the hopping of bosonic holons. The low-lying emergent gauge fields
associated with such a specific fractionalization are of mutual Chern-Simons
type. Corresponding to this superconducting ground state, three types of
elementary excitations are identified. Among them a Bogoliubov nodal
quasiparticle is conventional, while the other two are neutral excitations of
non-BCS type that play crucial roles in higher energy/temperaure regimes. Their
unique experimental implications for the cuprates are briefly discussed.Comment: 22 pages, 2 figure
The effect of strength-endurance training on serum and urine metabolic profiles of female adolescent volleyball athletes
Enhancement of the superconducting transition temperature from the competition between electron-electron correlations and electron-phonon interactions
We uncover that the competition between electron-electron correlations and
electron-phonon interactions gives rise to unexpectedly huge enhancement of the
superconducting transition temperature, several hundreds percent larger (
200 K) than that of the case when only one of the two is taken into account
( 30 K). Our renormalization group analysis claims that this mechanism
for the enhancement of the critical temperature is not limited on
superconductivity but applied to various Fermi surface instabilities, proposing
an underlying universal structure, which turns out to be essentially identical
to that of a recent study [Phys. Rev. Lett. {\bf 108}, 046601 (2012)] on the
enhancement of the Kondo temperature in the presence of Rashba spin-orbit
interactions. We also discuss the stability of superconductivity against
nonmagnetic randomness
Spin Tunneling in Magnetic Molecules: Quasisingular Perturbations and Discontinuous SU(2) Instantons
Spin coherent state path integrals with discontinuous semiclassical paths are
investigated with special reference to a realistic model for the magnetic
degrees of freedom in the Fe8 molecular solid. It is shown that such paths are
essential to a proper understanding of the phenomenon of quenched spin
tunneling in these molecules. In the Fe8 problem, such paths are shown to arise
as soon as a fourth order anisotropy term in the energy is turned on, making
this term a singular perturbation from the semiclassical point of view. The
instanton approximation is shown to quantitatively explain the magnetic field
dependence of the tunnel splitting, as well as agree with general rules for the
number of quenching points allowed for a given value of spin. An accurate
approximate formula for the spacing between quenching points is derived
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